The present invention relates to an electrical control device which permits the control of any electrical load, regardless of load impedance. The invention has particular application to the dimming of fluorescent lights.
The ability to modulate illumination levels on a continuously variable basis has long been desirable for a number of reasons. These vary from convenience and aesthetics in homes and restaurants to the potential for saving energy in commercial and other establishments where lighting is a major user of electric power.
In the case of stores and large offices, light levels higher than needed offer a double energy penalty. Not only does the lighting consume more power than necessary, but this heat energy then must be removed by air conditioning, another major user of energy. In many large buildings, the heat provided by lighting and the occupants requires air conditioning even in the winter. For such installations, fluorescent and other gaseous lighting has been found to be much more economic than the very much less efficient incandescent lights. It is rare to find incandescent lighting used extensively in commercial, institutional, or office locations.
Many building managers and other managers who are conscious of cost and energy have attempted measures to reduce or modulate the light levels so as to provide only the needed amount of light. Throughout the corridors of many buildings, many of the fixtures have been removed from service. In other cases, occupants of offices having outside windows are urged to turn off their lights when light from the windows is sufficient. In other buildings, there are switching arrangements providing a level of illumination for after-hours periods which is lower than that during working hours. This is to permit cleaning personnel and occasional occupants to pass through the areas safely.
In offices where video display tubes (VDT's) are used, there is a persistent problem of establishing an ambient light level compatible with both the luminescent level of the VDT's and illumination of the papers and printed matter associated with the use of word processors and computers. Many offices report unnecessary fatigue because of the inability to control illumination levels.
In order to be able to better manage these lighting levels, it is desirable to be able to control or modulate the power to this lighting, just as can be done with the dimming controls available for incandescent lights. These latter controls have become popular and are used in many places. However, their use for controlling gaseous tube fixtures, such as standard fluorescent lights, produces unsatisfactory results. This is because the fluorescent tube, with an associated ballast, is a reactive load which cannot be controlled effectively and reliably by a standard dimmer control.